Continuous renal replacement techniques are often utilized to manage acid-base and electrolyte problems in the critically ill patient. These techniques have an inherent capacity to manipulate the plasma composition and can be utilized efficiently to maintain homeostasis and metabolic control. Unfortunately, the efficacy of these techniques also permits wide variation in their use and can result in complications if they are not used appropriately. In most instances complications can be prevented by recognition of the operating principles and careful attention to detail. This article provides an overview of the principles of acid-base and electrolyte management with continuous renal replacement therapy.